Spectroscopy utilizing inelastically scattered light, including fluorescence and Raman spectroscopy, has been explored as a technique for medical diagnosis. Promising results have been reported using tissue autofluorescence and Raman emissions to detect a diversity of diseases, such as occlusions including atherosclerosis in the vascular system including peripheral and coronary arteries, and precancerous or cancerous lesions in colon and bladder wall. Rapid in vivo methods of diagnosis based on fluorescence, Raman, and other spectral analysis methods will provide important diagnostic advances.
A majority of the diagnostic methods employed with inelastically scattered light utilize empirical algorithms derived from studying a limited number of specimens. Such empirical algorithms generally fail to utilize the wealth of biochemical and/or morphological information contained in the tissue spectrum. With fluorescence spectroscopy, for instance, part of the difficulty has been that fluorescence spectra observed from optically thick tissue is distorted from the intrinsic spectra of individual fluorescence fluorophores by the interplay of factors such as scattering, absorption, device geometry and tissue boundary conditions. Thus, experiments utilizing optical fiber probes in the clinical setting will often yield results different from those utilizing a laboratory spectrofluorimeter. In addition, the experimental data also depend on whether the tissue-environment boundary condition is index-matched or index-mismatched. Raman spectroscopy is affected in a similar manner.
A need exists, therefore, for methods of obtaining and analyzing optical information retrieved from tissue under study, both in vitro and in vivo, that provides more complete and uniform characterization of the tissue to aid in diagnosis.